1. Field of the Invention
The present invention relates to a method for forming end-face electrodes, and in particular relates to a method for forming end-face electrodes with solder on an end-face of a substrate having electronic components such as module components mounted thereon.
2. Description of the Related Art
FIG. 18 is a plan view of a master substrate used in a conventional forming method of end-face electrodes. A master substrate 1 has plural linear gaps 2 formed thereon. With these gaps 2, plural rectangular module substrates 3 are formed on the master substrate 1 and a waste substrate 4 is formed therearound. On an end face of the module substrate 3, which opposes the waste substrate 4 interposing the gap 2 therebetween, plural side electrodes 5 are formed with spacing between adjacent electrodes 5. On the module substrate 3, electrode patterns (not shown) are formed. Then, electronic components (not shown) are mounted on the module substrate 3, so that the electronic components and the electrode patterns are connected together so as to form circuits. In order to connect the circuits formed in such a manner to an external circuit, the electrode patterns are connected to the side electrodes 5 formed at ends of the module substrate 3.
To the side electrode 5 of the module substrate 3, an end-face electrode being convex relative to the master substrate 1 is formed with solder. For that purpose, as is shown in FIG. 19, a jig for fixation 6 is placed for fixing a solder solid on the master substrate 1. In addition, the master substrate 1 is coated with flux in advance. In the jig for fixation 6, a through-hole 7 is formed at a position corresponding to the side electrode 5, and a spherical solder solid 8 is inserted into the through-hole 7. By heating the solder solid 8 in this state, it is melted so as to hang down from the side electrode 5. Then, by cooling the master substrate 1, an end-face electrode 9 is formed to the side electrode 5 with solder, as shown in FIG. 20.
By cutting the master substrate 1 after forming the end-face electrodes 9, plural module components are obtained. At this time, the waste substrate 4 is removed. When mounting the module component obtained in such a manner on a motherboard, the end-face electrode 9 is placed on an electrode formed on the motherboard, to which the module component is connected by reflow.
In the conventional method for forming end-face electrodes, however, because the jig for fixation is used for arranging a solder solid in a position at which the side electrode is formed, a positional shift of the solder solid or non-contact between the side electrode and the solder solid occur if a position of the side electrode and a through-hole of the jig for fixation do not correspond completely to each other. Therefore, there may be cases where an end-face electrode of solder is not formed to the side electrode.
The solder solid is heated for melting in a state in which the jig for fixation overlaps with the master substrate, so that a number of jigs are required in mass production of module components. At this time, thermal deformation of the jig for fixation may occur. During heat treatment, flux may stick to the jig for fixation. When the jig for fixation is thermally deformed or the flux sticks to the jig, end-face electrodes may not be formed properly.
Accordingly, it is a principal object of the present invention to provide a method for forming end-face electrodes in which the end-face electrode of solder can be securely formed at a location in which a side electrode is formed and it can be formed without being affected by a jig for fixing solder solids. Moreover, the present invention provides a method for forming end-face electrodes in which a substrate having solder solids held at precise positions without using a jig for fixing solder solids can be heat-treated.
A method for forming end-face electrodes according to the present invention comprises the steps of preparing a substrate having gaps with side electrodes, each side electrode being formed at one of side ends opposing each other via the gap, pressing a solder solid into the gap of the substrate in order to hold the solder solid in the area where the side electrode is provided within the gap, and forming an end-face electrode on the side electrode by heating the substrate to melt the solder solid such that the end-face electrode protrudes from the substrate surface.
In the method for forming end-face electrodes, a part of the solder solid or the whole of the solder solid may be pressed into the gap.
It is preferable that hollows be formed at least at the end of the substrate in which the side electrode is formed.
It is also preferable that flux or solder paste be applied in the area into which the solder solid is pressed after the solder solid is pressed into the gap.
By pressing the solder solid into the gap of the substrate, the solder solid can be securely held to the part in which the side electrode is formed. Therefore, by melting the solder solid held in the gap, the end-face electrode made from solder protruding from the substrate surface can be formed in the side electrode with certainty.
When pressing the solder solid into the gap, a part of the solder solid or the whole of the solder solid may be pressed into the gap as long as the solder solid is held in contact with the side electrode. At this time, the solder solid may be deformed or may be held in a substantially non-deformed state.
By forming the hollow at the end of the substrate in which the side electrode is formed, the solder solid can be positioned by the hollow. At this time, the hollow may be formed in the part opposing the side electrode via the gap.
After the solder solid is pressed into the gap, the solderability of the solder solid to the side electrode is improved by coating it with flux when melting the solder solid, enabling the end-face electrode to be securely formed in the side electrode. Furthermore, when using solder paste instead of the flux, while electronic components are mounted on the substrate so as to be connected to the side electrode, the end-face electrode can be formed in the side electrode. After pressing the solder solids into hollows, the end-face electrodes may be formed by applying a solder paste. Electronic components to be mounted on the substrate can be soldered to electrode patterns by the solder paste. By using the solder paste, two steps of forming the end-face electrodes and mounting the electronic components can be performed at the same time. This enables reduction of the number of manufacturing processes and cost.
According to the present invention, a method for forming end-face electrodes may further comprise the steps of preparing a distribution plate in which holes for distributing solder solids are provided at locations corresponding to portions where the side electrodes are formed, placing the distribution plate onto the substrate, distributing solder solids into the gaps through the holes for distributing of the distributing plate, and pressing the solder solids into the gaps from above the distributing plate.
In such a method for forming end-face electrodes, the pressing the solder solids into the gaps may be performed with a roller from above the distribution plate after placing the distribution plate onto the substrate.
Also, the pressing the solder solids into the gaps may be performed with a planar plate from above the distribution plate after placing the distribution plate onto the substrate.
Also, the pressing the solder solids into the gaps may be performed with a pressing plate having projections corresponding to the holes for distributing by inserting the projections into the holes for distributing after placing the distribution plate onto the substrate.
It is preferable that when pressing solder solids into the substrate by using the roller or the planar plate, the distribution plate be removed after the solder solids are pressed into the gaps of the substrate, and the pressing be performed again from above the solder solids as principal pressing.
By using the distribution plate having holes for distributing solder solids, solder solids can be distributed into the gaps of the substrate at positions where the side electrodes are formed. In this state, by pressing the solder solids into the gaps from above the distribution plate, the solder solids can be held at precise positions. Thereafter, the solder solids are melted by the heat-treatment of the substrate, so that the end-face electrodes protruding with respect to the substrate are formed. Since the solder solids are pressed at the precise positions of the substrate, a jig for fixing solder solids is not required during the heat-treatment of the substrate. This eliminates the effect due to a warp of the jig for fixation, etc., resulting in reduction of defects in forming the end-face electrodes.
The pressing of the solder solids into the gaps may be performed with the roller from above the distribution plate or with the planar plate. Also, the solder solids may be pressed into the gaps by using the pressing plate having projections formed by corresponding to the holes for distributing so as to insert the projections into the holes for distributing.
When only the pressing from above the distribution plate is insufficient, the principal pressing may be performed so as to completely press the solder solids into the gaps after removing the distribution plate.
According to the present invention, by pressing solder solids into recesses formed on a module substrate, the solder solids can be held in contact with side electrodes formed on the module substrate securely. Therefore, end-face electrodes can be formed on the side electrodes with certainty by melting the solder solids. Also, because a jig for positioning solder solids is not required, flux cannot adhere to the jig, so that a defect for forming end-face electrodes due to the jig is not produced, resulting in improving yield in forming end-face electrodes.
Furthermore, when end-face electrodes are formed by printing solder paste after pressing solder solids into the recesses, electronic components mounted on the substrate with solder paste can be soldered to electrode patterns. In such a manner, by using the solder paste, the forming of the end-face electrodes and the mounting of the electronic components can be simultaneously performed, enabling reduction in the number of manufacturing processes and cost down of module components to be achieved.
According to the present invention, during forming end-face electrodes on a substrate, solder solids can be pressed at precise positions of the substrate in gaps formed on the substrate. Therefore, when melting solder solids by the heat-treatment of the substrate, a jig for fixing solder solids is not required. Thereby, the effect due to a warp of the jig for fixation produced during the heat-treatment is eliminated, preventing defects in forming end-face electrodes.
These and other objects, features, and effects of the present invention will become more apparent from the following embodiments of the present invention described in detail with reference to the drawings.